The present invention relates generally to pull-type implements and more particularly to a mechanism for resisting the side draft forces commonly encountered by such implements.
Many pull-type implements such as windrowers include a fore-and-aft extending drawbar and a transversely extending harvesting unit projecting from one side of the drawbar. The offset harvesting unit permits the operator to drive adjacent to the crop while harvesting it with the transversely extending harvesting unit. Since the harvesting unit projects from one side of the drawbar, its outer end will tend to fall back during harvesting and generate side draft forces on the implement. In hilly-type fields, the outer end often falls back significantly as the unit proceeds up the hill.
As farm implements have become wider and larger, windrowers in excess of 25 feet in width have become common. The fallback problem with such harvesting units has accordingly increased. When fallback does occur, the swath of crop harvested becomes narrower and uneven. In some cases the harvesting unit is not able to cut the crop due to the angle of approach. When the harvested width is irregular, subsequent additional operations, such as picking up a windrowed crop with a combine, would become difficult and result in a loss of crop and also productivity.
In an attempt to overcome the fall back problem, some machines have been provided with double wheels at the outer end of the harvesting unit to improve flotation and reduce the rolling resistance of each wheel. While some improvement is realized with this arrangement, there nevertheless remains sufficient drag to cause the outer end of the unit to frequently fall back, particularly when the implement is used to harvest hilly fields.
Another approach utilized to minimize the fallback problem has been the use of powered wheels at the outer end of the harvesting unit. With this solution, an electromagnetic switch is often provided at the hitch connection between the tractor and the implement drawbar. The switch registers the angular disposition of the drawbar relative to the tractor. When a significant degree of fallback occurs, the switch activates the driven outer wheels to bring the harvester back to its appropriate position transverse to the line of travel. This solution is expensive and the switch is often sensitive to environmental contamination prevalent in harvesting operations. As a result the driven wheels are frequently activated and shut off in an attempt to maintain the outer end of the harvesting unit perpendicular to the line of travel. Since it is common to provide powered wheels driven at a speed in excess of the average forward travel speed of the harvester, the driven end of the harvesting unit will constantly seek to remain perpendicular to the line of travel.